Modulated carrier wave transmitter



Get. 15, 1935. w DlTcHAM 2,017,118

MODULATED CARRIER WAVE TRANSMITTER Filed April 9, 1954 INVENTOR MAL/AM 7? 0/76/7444! ATTORNEY Patented Oct. 15, 1935 UNITED STATES PATENT OFFICE MODULATED CARRIER. WAVE TRANS- MITTER Application April 9, 1934-, Serial No. 719,632

. In Great Britain April 27, 19331 4 Claims,

This invention relates to modulated carrier wave transmitters suitable for use for wireless signalling.

The invention has for its object to provide a modulated carrier wave transmitter which shall give amplitude modulated output currents or voltages but which shall be such that the high power thermionic valves in the transmitter may be utilized at a high efficiency.

As is well known the method of phase modulation presents practical advantages of substance so far as the efficient utilization of thermionic valves is concerned, while amplitude modulation provides other well known practical advantages and is moreover a method of modulation at present in very common use; for example, the majority of broadcast receivers are adapted to receive amplitude modulated energy but will not, without alteration, receive phase modulated energy.

The present invention may be regarded as providing a transmitter having many advantages ordinarily only associated with phase modulated transmitters and yet giving an amplitude modulated output.

According to this invention an amplitude modulated carrier wave transmitter comprises means for obtaining phase modulated carrier wave energy of. substantially constant amplitude, means for applying said phase modulated energy difierentially to the input circuits of two thermionic amplifiers said input circuits including in the one case a phase retarding element and in the other case a phase advancing element, and means for combining the outputs from the said amplifiers in a common load circuit whereby the phase modulated energy is transformed into amplitude modulated energy in said load circuit.

Although in the above statement of invention and in the description and claims which follow, reference is made to means for producing phase modulated energy of substantially constant amplitude and applying it differentially to the input circuits of the combined amplifiers, it will be apparent to those skilled in the art that two separate but similar sources of phase modulated energy may be utilized if desired providing that they be of precisely similar carrier frequency and similarly modulated, and it is to be understood that such arrangements are intended to be included in the present invention and it will be appreciated that the use of two of such similar phase modulated sources of energy and the application thereof in opposition to the combining valve stages is, from the viewpoint of the present invention equivalent to the provision of a single source and its application diiierentially tothe said stages.

In a preferred arrangement in accordance with this invention, a modulated carrier wave transmitter comprises a load circuit, such for example as an aerial circuit; two thermionic amplifiers coupled or connected to said load circuit in such manner that the power developed by said amplitiers adds in said load circuit; sources of modulating energy and carrier energy; means for modulating the phase of the carrier energy with the modulating energy toproduce two differentially phase modulated carrier energies; means for applying one of the phase modulatedenergies, as an input to one of the said two amplifiers; means for applying the other phase modulated energy as an input to the other of said two amplifiers; means for fixedly advancingthe phase in one of said amplifiers; and means for fixedly retarding the-phase in the other. It will thus be seen that the whole arrangementis such that phase modulated energy is transformed into amplitude modu Iatedenergy the two valve amplifiers feeding the load circuit being so arranged that were the phase advancing and phase retarding elements associated therewith omitted, the currentprovided bythe two amplifiers in theload circuit would be zero.

The invention is illustrated in the drawing accompanying the specification. The drawing shows diagrammatically one circuit arranged in accordance with my invention.

Referring to the drawing, carrier wave input from a master oscillator, or any other source of carrier waves, is applied to the primary winding I of a transformer whose secondary winding- 2 is tuned by a capacity in the usual way and is connected tosupply carrier input to the control grids of fourscreened grid valves VI V2, V3, V4. Connected in the gridcircuit of the valves VI and V2 are phase retarding elements constituted by inductances LI and L2 and connected in the grid circuits of the valves V3 and V4 are phase advancing condensers CI C2. Modulating potentials are applied to the primary winding 3 of a transformer whose secondary winding 4 is connected to apply modulating potentials to four modulator valves MVI, MV2, MV3, MV4 the valves MVI and MV 2 having their control grids in to the circuit AGZ.

systems in differential arrangement is followed' by two further thermionic valves AVI and AVZ having tuned grid circuits AGI and AGZ, the grid circuit AGI being connected to the control grid of the valve AVI through a phase retarding inductance L3 and the circuit AGZ being connected to the control grid of the valve AVZ through a phase advancing condenser. C3. Thus phase modulated potentials from the circuit PMI are applied to the circuit AG! and phase modulated potentials from the circuit PMZ are applied- The valves AVI and AV2 are similar and the phase retardation effected by the inductance L3 is equal and opposite to the phase advance effected by the condenser C3 and, the whole arrangement is preferably symmetrical about the earth point. The anodes of the valves AVI, AVZ are, coupled cumulatively so that their energies add in a load circuit illustrated as'including an aerial A and it will be apparent that assuming constant amplitude differentially phase modulated, energy to be set up in the circuits PMI and PMZ simple amplitude modulated energy will be radiated from the aerial A. y

In carrying out this invention other means than that shown may be employed forproducing the desired phase modulation in what may be termed the intermediate amplifiers.

Of course the actual number of amplifying stages provided depends upon individual requirements. For example, one or more amplifiers may be interposed between the phase modulated amplifiers and the final amplifiers valves AVI and AVZ or between the phase modulated amplifiers and the master oscillator (not shown) and again any of the single valves shown in the figure may be replaced by'a plurality of valves in parallel,

Having now particularly described and ascer tained the nature of my said invention and in what manner the same is to be performed, I declare that what I claim is: r

1. An amplitude modulated transmitter comprising means for obtaining phase modulated carrier wave energy of substantially constant amplitude, means for applying said phase modulated energy in two similar portions diiferentially to the input circuits of two thermionic amplifiers, said input circuits including in the one case a phaseretarding element and in the other case a phase advancing element, and means for combining the outputs from the said amplifiers in a common load circuit whereby the phase modulated energy is transformed into amplitude modulated energy in said load circuit.

2. An amplitude modulated carrier wave transmitter comprising a load circuit, two thermionic 6 carrier energy, means for modulating the phase 10- of the carrier energy with the modulating energy to produce two differentially phase modulated carrier energies, means for applying one of the phase modulated energies to the input of one of the said two amplifiers, means for applying the 15 other phase modulated energy to the input of the: other of said two 'amplifiers, said first named means including means for fixedly advancing the phase on the input of one of said amplifiers, and said second named means including means for 20 fixedly retarding by a like amount the phase on the input of the other of said amplifiers.

3. A transmitter comprising a source of carrier frequency oscillations, means for applying said oscillations through a phase retarding element tothe 25 control grid of a high frequency thermionic amplifiervalve stage, means for applying said oscillations inopposite sense through a phase advancing element quantitatively equal to said phase retarding element to the control grid of a second 30 high frequency thermionic amplifier valve stage,

a source of modulating potentials, means for applying said modulating potentials differentially to the grids of apair of modulating valve stages associated each with one of said high frequency 35 amplifier valve stages, an additional pair of further high frequency valve amplifier stages, means for applying phase modulated energy from the output circuits of said first mentioned high fre, quency amplifier stages differentially to the grid 40 circuits of said further amplifier valve stages, quantitatively equal phase advancing and phase retarding means connected each in the grid circuit of one orother of said additional high frequency amplifier valve stages, and a common load 4 circuit driven from the output circuits of said further high frequency amplifiers, the whole arrangement being such that amplitude modulated energy occurs in said common load circuit.

LA transmitter as recited in claim 3 and 50.

the modulating 'valve stages are similarly to- 55:

gether constituted by four valves or four parallel connected Valve banks two in parallel and two in push-pull substantially as described.

WILLIAM THEODORE DITCI-IAM. 00. 

